Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.49   10.624%   $59.1728   $59.17   $59.15   $59.20  
  Purchase #2 $238.40   9.171%   $260.2637   $260.26   $260.25   $260.30  
  Purchase #3 $212.81   5.277%   $224.04   $224.04   $224.05   $224.00  
  Purchase #4 $42.46   7.652%   $45.709   $45.71   $45.70   $45.70  
  Purchase #5 $47.99   5.647%   $50.7   $50.70   $50.70   $50.70  
  Purchase #6 $170.34   10.449%   $188.1388   $188.14   $188.15   $188.10  
  Purchase #7 $33.53   3.256%   $34.6217   $34.62   $34.60   $34.60  
  7 purchase totals = $799.02       $862.6460   $862.64   $862.60   $862.60